Etching of thin damage sensitive layers using high frequency pulsed plasma

Abstract

Disclosed is a system for etching thin damage sensitive layers with a plasma. The invention finds particular application for etching damage sensitive thin films such as Gallium Arsenide on Aluminum Gallium Arsenide. Damage to sensitive thin films is avoided by lowering the DC bias of the cathode. The low DC bias is achieved by increasing the frequency of the power source producing the plasma. A reduced etch rate, suitable for etching thin layers, is achieved by pulsing the RF power source between a high power and a low power at a selected duty cycle.

What is claimed is:  
     
         1 . A plasma reactor for processing a substrate comprising: 
 a vacuum chamber;    a first electrode for supporting the substrate within said vacuum chamber;    a second electrode being grounded;    a process gas;    a pulsable radio frequency power source electrically coupled to the first electrode and applying a voltage thereto for converting the process gas into a plasma having charged particles and activated neutral species, the pulsable radio frequency power source operating at a frequency that is greater than 13.56 MHz, generation of the plasma causing a self biasing of the first electrode, the self biasing being reduced by operating at the increased frequency of the radio frequency power source; and    wherein the pulsable radio frequency power source is cycled between a high power and a low power at a selected duty cycle.    
     
     
         2 . The system as described in  claim 1  wherein the duty cycle is less than 50%.  
     
     
         3 . The system as described in  claim 1  wherein the duty cycle is between 5-30%.  
     
     
         4 . The system as described in  claim 1  wherein the pulsable radio frequency power source is pulsed on and off at a selected duty cycle.  
     
     
         5 . The system as described in  claim 4  wherein the duty cycle is less than 50%.  
     
     
         6 . The system as described in  claim 4  wherein the duty cycle is between 5-30%.  
     
     
         7 . The system as described in  claim 1  wherein the frequency of the radio frequency power source is selected such that the self biasing of the first electrode |V dc | is less than 50 volts.  
     
     
         8 . The system as described in  claim 1  wherein the frequency of the radio frequency power source is 40.68 MHz.  
     
     
         9 . A plasma reactor for processing a substrate comprising: 
 a vacuum chamber;    a first electrode for supporting the substrate within said vacuum chamber;    a second electrode being grounded;    a process gas; and    a radio frequency power source coupled to the first electrode and applying a voltage thereto for converting the process gas into a plasma having charged particles and activated neutral species, the radio frequency power source operating at a frequency that is greater than 13.56 MHz, generation of the plasma causing a self biasing of the first electrode, the self biasing being reduced by operating at the increased frequency of the power source.    
     
     
         10 . The system as described in  claim 9  wherein the power source is a radio frequency power source operating at 40.68 Mhz.  
     
     
         11 . The system as described in  claim 9  wherein the frequency is selected to produce a DC bias |V dc | of less than 50 volts.  
     
     
         12 . A plasma reactor for processing a substrate comprising: 
 a vacuum chamber;    a first electrode for supporting the substrate within said vacuum chamber;    a second electrode being grounded;    a process gas;    a pulsable radio frequency power source coupled to the first electrode and applying a voltage thereto for converting the process gas into a plasma having charged particles and activated neutral species, the radio frequency power source operating at a frequency of 13.56 MHz; and    wherein the pulsable radio frequency power source is cycled between a high power and a low power at a selected duty cycle.    
     
     
         13 . The system as described in  claim 12  wherein the duty cycle is less than 50%.  
     
     
         14 . The system as described in  claim 12  wherein the duty cycle is between 5-30%.  
     
     
         15 . The system as described in  claim 12  wherein the pulsable radio frequency power source is pulsed on and off at a selected duty cycle.  
     
     
         16 . The system as described in  claim 15  wherein the duty cycle is less than 50%.  
     
     
         17 . The system as described in  claim 15  wherein the duty cycle is between 5-30%.  
     
     
         18 . A plasma reactor for processing a substrate comprising: 
 a vacuum chamber;    a first electrode for supporting the substrate within said vacuum chamber;    a second electrode being grounded;    a process gas;    a first radio frequency power source coupled to the first electrode and applying a voltage thereto for converting the process gas into a plasma having charged particles and activated neutral species, the first radio frequency power source operating at a frequency that is greater than 13.56 Mhz, generation of the plasma causing a self biasing of the first electrode, the self biasing being reduced by operating at the increased frequency of the first radio frequency power source;    an induction coil adjacent to at least a portion of the vacuum chamber, the induction coil operatively coupled to a pulsable radio frequency power source to inductively couple power into the vacuum chamber to produce at least one plasma; and    wherein the pulsable radio frequency power source is cycled between a high power and a low power at a selected duty cycle.    
     
     
         19 . The system as described in  claim 18  wherein the duty cycle is less than 50%.  
     
     
         20 . The system as described in  claim 18  wherein the duty cycle is between 5-30%.  
     
     
         21 . The system as described in  claim 18  wherein the pulsable radio frequency power source is pulsed on and off at a selected duty cycle.  
     
     
         22 . The system as described in  claim 21  wherein the duty cycle is less than 50%.  
     
     
         23 . The system as described in  claim 21  wherein the duty cycle is between 5-30%.  
     
     
         24 . The system as described in  claim 18  wherein the self biasing of the first electrode |V dc | is less than 50 volts.  
     
     
         25 . The system as described in  claim 18  wherein the radio frequency of the first radio frequency power source is 40.68 MHz.  
     
     
         26 . A method for etching a semiconductor substrate comprising: 
 placing the semiconductor substrate on a first electrode in a vacuum chamber;    providing a process gas to the vacuum chamber;    introducing a radio frequency power coupled to the first electrode at a frequency greater than 13.56 MHz into the vacuum chamber to produce a plasma from the process gas, generation of the plasma causing a self biasing of the first electrode, the self biasing being reduced by operating at the increased frequency of the radio frequency power source;    pulsing the radio frequency power source between a high power and a low power at a selected duty cycle; and    exposing the semiconductor substrate to the plasma.    
     
     
         27 . The method as described in  claim 26  wherein the duty cycle is less than 50%.  
     
     
         28 . The method as described in  claim 26  wherein the duty cycle is between 5-30%.  
     
     
         29 . The method as described in  claim 26  wherein the pulsable radio frequency power source is pulsed on and off at a selected duty cycle.  
     
     
         30 . The method as described in  claim 26  wherein the duty cycle is less than 50%.  
     
     
         31 . The method as described in  claim 29  wherein the duty cycle is between 5-30%.  
     
     
         32 . The method as described in  claim 29  wherein the frequency is selected to produce a DC bias |V dc | of less than 50 volts.  
     
     
         33 . The method as described in  claim 26  wherein the radio frequency of the power source is 40.68 MHz.  
     
     
         34 . The method as described in  claim 26  wherein the substrate further comprises at least one indium containing layer.  
     
     
         35 . The method as described in  claim 26  wherein the substrate further comprises at least one gallium containing layer.  
     
     
         36 . The method as described in  claim 35  wherein the substrate further comprises at least one aluminum containing layer.  
     
     
         37 . A method for etching a semiconductor substrate comprising: 
 placing the semiconductor substrate on a first electrode in a vacuum chamber;    providing a process gas to the vacuum chamber;    introducing a radio frequency power coupled to the first electrode at a frequency greater than 13.56 MHz into the vacuum chamber to produce a plasma from the process gas, generation of the plasma causing a self biasing of the first electrode, the self biasing being reduced by operating at the increased frequency of the radio frequency power source; and    exposing the semiconductor substrate to the plasma.    
     
     
         38 . The method as described in  claim 37  wherein the radio frequency of the power source is 40.68 MHz.  
     
     
         39 . The method as described in  claim 37  wherein the frequency is selected to produce a DC bias |V dc | of less than 50 volts.  
     
     
         40 . The method as described in  claim 37  wherein the substrate further comprises at least one indium containing layer.  
     
     
         41 . The method as described in  claim 37  wherein the substrate further comprises at least one gallium containing layer.  
     
     
         42 . The method as described in  claim 41  wherein the substrate further comprises at least one aluminum containing layer.  
     
     
         43 . A method for etching a semiconductor substrate comprising: 
 placing the semiconductor substrate on a first electrode in a vacuum chamber;    providing a process gas to the vacuum chamber;    introducing a radio frequency power coupled to the first electrode at a frequency of 13.56 MHz into the vacuum chamber to produce a plasma from the process gas;    introducing a pulsed radio frequency power source into the vacuum chamber, the pulsed radio frequency power source being cycled between a high power and a low power at a selected duty cycle; and    exposing the semiconductor substrate to the plasma.    
     
     
         44 . The method as described in  claim 43  wherein the duty cycle is less than 50%.  
     
     
         45 . The method as described in  claim 43  wherein the duty cycle is between 5-30%.  
     
     
         46 . The method as described in  claim 43  wherein the pulsable radio frequency power source is pulsed on and off at a selected duty cycle.  
     
     
         47 . The method as described in  claim 46  wherein the duty cycle is less than 50%.  
     
     
         48 . The method as described in  claim 46  wherein the duty cycle is between 5-30%.  
     
     
         49 . The method as described in  claim 43  wherein the substrate further comprises at least one indium containing layer.  
     
     
         50 . The method as described in  claim 43  wherein the substrate further comprises at least one gallium containing layer.  
     
     
         51 . The method as described in  claim 50  wherein the substrate further comprises at least one aluminum containing layer.  
     
     
         52 . A method for etching a semiconductor substrate comprising: 
 placing the semiconductor substrate on a first electrode in a vacuum chamber;    providing a process gas to the vacuum chamber;    introducing a first radio frequency power coupled to the first electrode at a frequency greater than 13.56 MHz into the vacuum chamber to produce a plasma from the process gas, generation of the plasma causing a self biasing of the first electrode, the self biasing being reduced by operating at the increased frequency of the first radio frequency power source;    introducing a second radio frequency power coupled to an induction coil adjacent to at least a portion of the vacuum chamber to produce at least one plasma;    pulsing the second radio frequency power source such that the power to the induction coil alternates between a high power and a low power at a selected duty cycle; and    exposing the semiconductor substrate to the plasma.    
     
     
         53 . The method as described in  claim 52  wherein the duty cycle is less than 50%.  
     
     
         54 . The method as described in  claim 52  wherein the duty cycle is between 5-30%.  
     
     
         55 . The method as described in  claim 52  wherein the pulsable radio frequency power source is pulsed on and off at a selected duty cycle.  
     
     
         56 . The method as described in  claim 55  wherein the duty cycle is less than 50%.  
     
     
         57 . The method as described in  claim 55  wherein the duty cycle is between 5-30%.  
     
     
         58 . The method as described in  claim 52  wherein the frequency of the first radio frequency power source is selected to produce a DC bias |Vdc| of less than 50 volts.  
     
     
         59 . The method as described in  claim 52  wherein the radio frequency of the first radio frequency power source is 40.68 MHz.  
     
     
         60 . The method as described in  claim 52  wherein the substrate further comprises at least one indium containing layer.  
     
     
         61 . The method as described in  claim 52  wherein the substrate further comprises at least one gallium containing layer.  
     
     
         62 . The method as described in  claim 61  wherein the substrate further comprises at least one aluminum containing layer.